A lead frame is manufactured by stamping a plate-formed lead frame material made of copper, iron, or alloy containing one of these metals as a main component (such as Fe--Ni alloy) into a specified form, and generally comprises a die bonding section, an inner lead section, and an outer lead section.
A semiconductor chip is die-bonded to a die bonding section of a lead frame, for instance, by means of the Au-Si autectic method, by bonding with Ag paste or the line, or by bonding with soldering, a lead section (an electrode section) and an inner lead section of the semiconductor chip are wire-bonded using Au or A1 wire, then molding is carried out by shielding with resin (or ceramics) leaving the outer lead section, thus a mold pack semiconductor device being manufactured.
A mold pack semiconductor device is mounted on an electronic board for use by bending an outer lead section thereof and inserting the bent outer lead section into the electronic board or the like.
By the way, adhesion between a semiconductor chip and a die bonding section or adhesion between an inner lead section and wire is an important problem. If the adhesion is poor, the wire may be peeled off during use of the mold pack semiconductor device, which may cause disconnection and give damages to reliability of the semiconductor device. Also in the molding process, the wire may be pealed off due to a pressure for shielding, which in turn may lower the yield.
To improve the adhesion, sometimes silver-plating is carried out to a portion of or the entire surface of the lead frame (especially a die bonding section and an inner lead section each subjected to bonding).
However, in a case where silver plating is executed to the entire surface of a lead frame, there occurs a problem that change of color is generated in a surface of the silver plating surface due to heating under a high temperature in a range from 200.degree. to 450.degree. C. in the processes of, for instance, die bonding, wire bonding, or shielding with resin. In recent years, various efforts have been performed for trying to prevent the color change due to heating under a high temperature by lowering the required temperature in the processes as described above, but the result is not adequate yet, and even if it is possible to prevent color change in the above-described processes, there still remains a problem that color change occurs in portions other than a section shielded with resin (i.e. an outer lead section) during storage thereof in the atmospheric air for several day. When this kind of color change is generated in the outer lead section, there occurs also a problem that variation in electric contact resistance between the outer lead section and a section in the electronic board into which the outer lead section is inserted is generated.
To solve the problem due to color change as described above, silver plating in the outer lead section is pealed off after molding has been finished, and then normally surface processing such as alloy plating or soldering plating in which tinning or tin is a standard composition is subjected thereto. It should be noted that, herein the reason why tinning is subjected to the outer lead section after silver plating has been pealed off once without coating tinning over the silver-plated layer is because, if silver plating layer is coated by tinning or the like, there occurs a problem that silver and tin are alloyed in association with elapse of time, which makes the outer lead section much brittle and gives damages to reliability of the mold pack semiconductor device.
However in the technology described above, process for pealing off a silver plating and process for surfaces to be subjected to tinning are required, and at least two days are required for those processes. In addition thereto, when hardness of tin or tin alloy is low and the outer lead section is repeatedly set to or taken off from the electronic board of the mold pack semiconductor device, there occurs also a problem that the outer lead section is easily worn out and variation in electric contact resistance is easily generated. It is an object of the present invention to provide a lead frame and a lead frame material which are possible to reduce largely required a number of days for manufacturing as compared to the conventional type thereof because bonding is under good conditions and processes such as tinning or the like are not required, and furthermore has high abrasion resistance.